This invention relates to an apparatus for preventing buckling of narrow members subjected to a compression load, and more particularly, it relates to an apparatus for preventing buckling of narrow members which are ordinarily loaded in tension but on occassion will be loaded in compression, such as hanger rods which are used for top supporting vapor generator components, or pipe truss members used in vapor generator ductwork.
A vapor generator is usually top supported in order to allow for downward expansion of its components, which expansion results from the absorption of heat by the components. A conventional top support system includes an external superstructure, laterally extending beams hung from the superstructure and a plurality of narrow hanger rods connected between the beams and the vapor generator. The hanger rods are normally subjected to a downward load, as a result of the weight of the vapor generator components pulling down on the rods, and are therefore normally under tension. Under normal operating conditions hanger rods not only provide top support for the unit but also prevent the roof from moving downwardly relative to the vapor generator enclosure walls and suspended elements which penetrate the roof at various locations. However if abnormally high positive pressure develops within the furnace enclosure, for example, if as a result of a furnace "PUFF", some hanger rods can be subjected temporarily to a compression load, and tend to buckle since they are relatively slender. Under such conditions the roof tends to move relative to the suspended elements, and seal plates attached between the roof and various suspended elements can be torn free. It is to be understood that seal plates may be designed to accommodate some relative movement, such as by forming corrugation in the plates, but such plates can ordinarily accommodate only the expected slight relative movement resulting from relative thermal expansion. Therefore, it is important that hanger rods be capable of withstanding a compression load in order to preclude relative movement between the roof and suspended elements, and thereby prevent against damaging associated seals.
In long sections of ductwork, such as the ductwork associated with the vapor generator convection section outlet, pipe trusses are often used to provide for structural integrity of the ductwork. During normal operation of the vapor generator there may be a negative pressure within this ductwork, and as a result some of the truss members would be subjected to a tensile load and others subject to a compression load. The truss members expected to be under a tensile load are usually slender pipes, whereas members expected to bear compression loads comprise members of a greater cross sectional area. If a positive pressure develops within the ductwork, those members expected to be in tension may be subjected to a compression load, and other members expected to be under compression may be subjected to a tensile load. The later members ordinarily are capable of withstanding a tensile load, but the slender members tends to buckle when loaded in compression. If these slender members do buckle, the relatively thin sheet metal walls defining the duct may collapse inwardly of the duct since the slender members do not act to resist the compression loading. Hence, as with narrow hanger rods, it becomes important to insure that slender truss members be capable of withstanding a compression load which may occur during periods of pressure excursions within the ductwork.
The instant invention provides means for preventing the buckling of narrow members, such as hanger rods, and/or truss members when they are subjected to a compression load. Therefore when used with a vapor generator top support system the invention precludes relative movement between the vapor generator components and prevents against consequent damage to associated seals, and when used with ductwork pipe trusses the invention precludes buckling of narrow truss members and thereby prevents against damaging the ductwork.